Ophthalmic device

ABSTRACT

An ophthalmic device that may include: a light source; a measurement optical system that generates measurement light; a first reference optical system that generates first reference light; a second reference optical system that generates second reference light; and an interference optical system that generates measurement interference light from the measurement light and the first reference light, and reference interference light from the first and second reference light. The measurement optical system may include a switching unit that switches between a first state in which the subject eye is irradiated with the light from the light source and a second state in which the light from the light source is guided to the second reference optical system branching from the measurement optical system. The controller may control the switching unit to detect the measurement interference light in the first state, and the reference interference light in the second state.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to Japanese Patent ApplicationNo. 2022-087144, filed on May 27, 2022, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The disclosure herein relates to ophthalmic devices configured tocapture tomographic images of a subject eye using an opticalinterference phenomenon.

BACKGROUND ART

In an ophthalmic device that uses an optical interference phenomenon,reference light and measurement light are combined to generatemeasurement interference light, and depthwise position information of asubject eye is calculated from the generated measurement interferencelight (for example, Japanese Patent Application Publication No.2012-161425).

SUMMARY

In order to accurately calculate depthwise position information in thistype of ophthalmic device, an optical path length of an optical systemthat generates reference light and measurement light needs to beadjusted accurately. For this purpose, calibration on the optical systemis performed at the time of manufacture of the ophthalmic device, andthe device is thereafter shipped out (that is, a calibration process isperformed at the time of shipping (more precisely, at the time ofoptical system calibration incorporated in a manufacturing procedure)).However, due to changes that occur in the optical path length of theoptical system due to post-shipment chronological change and/or anenvironment (such as temperature) at the time of measurement, there arecases in which measurement under the same condition as the calibrationprocess is difficult to achieve. To address this, consideration may begiven to correcting the depthwise position information of the subjecteye by generating reference light, which will be referred to as“correction reference light”, by splitting a part of light in aninterference optical system and using this correction reference light.

However, with such an ophthalmic device, a part of light from ameasurement optical system is emitted onto the subject eye to generatemeasurement light, and also a part of the light from the measurementoptical system is split to generate correction reference light. Then,depthwise position information of the subject eye calculated from themeasurement light is corrected using a reference position calculatedfrom the correction reference light. Due to this, there is a restrictionthat the reference position calculated from the correction referencelight needs to be set to a position different from that of the depthwiseposition information of the subject eye calculated from the measurementlight. The disclosure herein discloses art capable of setting areference position calculated from correction reference light at adesired position in an ophthalmic device that corrects depthwiseposition information of the subject eye using the correction referencelight.

A first ophthalmic device disclosed herein may comprise: a light source;a measurement optical system configured to generate measurement light byirradiating a subject eye with light from the light source; a firstreference optical system configured to generate first reference light byusing the light from the light source; a second reference optical systemconfigured to generate second reference light by using the light fromthe light source, the second reference light being used for calculatinga reference position; an interference optical system configured togenerate measurement interference light by combining the measurementlight and the first reference light and to generate referenceinterference light by combining the second reference light and the firstreference light; a detector configured to detect the measurementinterference light and output a measurement interference signal and todetect the reference interference light and output a referenceinterference signal; and a controller configured to calculate depthwiseposition information of the subject eye based on the measurementinterference signal and to calculate the reference position based on thereference interference signal. The second reference optical system mayinclude an optical path branching from the measurement optical system.The measurement optical system may comprise a switching unit configuredto switch between a first state and a second state, the first statebeing a state in which the subject eye is irradiated with the light fromthe light source and the second state being a state in which the lightfrom the light source is guided to the second reference optical system,and when the subject eye is measured, the controller may be configuredto control the switching unit to detect the measurement interferencelight with the detector in the first state, and to detect the referenceinterference light with the detector in the second state.

A second ophthalmic device disclosed herein may comprise: a first OCTconfigured to measure a first depthwise position of a first part of asubject eye; a second OCT configured to measure a second depthwiseposition of a second part of the subject eye, the second part beingdifferent from the first part; and a controller configured to calculatea depthwise length from the first part to the second part based on thefirst depthwise position measured by the first OCT and the seconddepthwise position measured by the second OCT. The first OCT maycomprise: a first light source; a first measurement optical systemconfigured to generate first measurement light by irradiating the firstpart of the subject eye with light from the first light source; a firstreference optical system configured to generate first reference light byusing the light from the first light source; a second reference opticalsystem configured to generate second reference light by using the lightfrom the first light source, the second reference light being used forcalculating a first reference position; a first interference opticalsystem configured to generate first measurement interference light bycombining the first measurement light and the first reference light andto generate first reference interference light by combining the secondreference light and the first reference light; and a first detectorconfigured to detect the first measurement interference light and outputa first measurement interference signal and to detect the firstreference interference light and output a first reference interferencesignal. The second reference optical system may include an optical pathbranching from the first measurement optical system, the firstmeasurement optical system my comprise a first switching unit configuredto switch between a first state and a second state, the first statebeing a state in which the subject eye is irradiated with the light fromthe first light source and the second state being a state in which thelight from the first light source is guided to the second referenceoptical system, and when the subject eye is measured, the first detectormay be configured to detect the first measurement interference lightwhile the first switching unit is in the first state, and to detect thefirst reference interference light while the first switching unit is inthe second state.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a configuration of optical systems of an ophthalmic deviceaccording to a first embodiment.

FIG. 2 shows a relationship of measurement areas of a subject eyemeasured by two OCTs of the ophthalmic device according to the firstembodiment.

FIG. 3 is a block diagram showing a configuration of a control system ofthe ophthalmic device according to the first embodiment.

FIG. 4 is a flowchart showing a procedure for measuring an axial lengthof the subject eye using the ophthalmic device according to the firstembodiment.

FIG. 5 shows a configuration of optical systems of an ophthalmic deviceaccording to a second embodiment.

FIG. 6 shows the configuration of the optical systems of the ophthalmicdevice according to the second embodiment (at the time of optical systemcalibration).

FIG. 7 shows the configuration of the optical systems of the ophthalmicdevice according to the second embodiment (at the time of subject eyemeasurement).

FIG. 8 is a block diagram showing a configuration of a control system ofthe ophthalmic device according to the second embodiment.

FIG. 9 is a flowchart showing a procedure for measuring the axial lengthof the subject eye using the ophthalmic device according to the secondembodiment.

DETAILED DESCRIPTION

Representative, non-limiting examples of the present disclosure will nowbe described in further detail with reference to the attached drawings.This detailed description is merely intended to teach a person of skillin the art further details for practicing preferred aspects of thepresent teachings and is not intended to limit the scope of the presentdisclosure. Furthermore, each of the additional features and teachingsdisclosed below may be utilized separately or in conjunction with otherfeatures and teachings to provide improved ophthalmic devices, as wellas methods for using and manufacturing the same.

Moreover, combinations of features and steps disclosed in the followingdetailed description may not be necessary to practice the presentdisclosure in the broadest sense, and are instead taught merely toparticularly describe representative examples of the present disclosure.

Furthermore, various features of the above-described and below-describedrepresentative examples, as well as the various independent anddependent claims, may be combined in ways that are not specifically andexplicitly enumerated in order to provide additional useful embodimentsof the present teachings.

All features disclosed in the description and/or the claims are intendedto be disclosed separately and independently from each other for thepurpose of original written disclosure, as well as for the purpose ofrestricting the claimed subject matter, independent of the compositionsof the features in the embodiments and/or the claims. In addition, allvalue ranges or indications of groups of entities are intended todisclose every possible intermediate value or intermediate entity forthe purpose of original written disclosure, as well as for the purposeof restricting the claimed subject matter.

Some of primary features of the first ophthalmic device and the secondophthalmic device as described above will be listed. The technicalelements described hereinbelow are each independent and capable ofachieving technical usefulness alone or in various combinations, andsuch combinations are not limited to those recited in the claims asoriginally filed.

A first ophthalmic device disclosed herein may comprise: a light source;a measurement optical system configured to generate measurement light byirradiating a subject eye with light from the light source; a firstreference optical system configured to generate first reference light byusing the light from the light source; a second reference optical systemconfigured to generate second reference light by using the light fromthe light source, the second reference light being used for calculatinga reference position; an interference optical system configured togenerate measurement interference light by combining the measurementlight and the first reference light and to generate referenceinterference light by combining the second reference light and the firstreference light; a detector configured to detect the measurementinterference light and output a measurement interference signal and todetect the reference interference light and output a referenceinterference signal; and a controller configured to calculate depthwiseposition information of the subject eye based on the measurementinterference signal and to calculate the reference position based on thereference interference signal. The second reference optical system mayinclude an optical path branching from the measurement optical system.The measurement optical system may comprise a switching unit configuredto switch between a first state and a second state, the first statebeing a state in which the subject eye is irradiated with the light fromthe light source and the second state being a state in which the lightfrom the light source is guided to the second reference optical system,and when the subject eye is measured, the controller may be configuredto control the switching unit to detect the measurement interferencelight with the detector in the first state, and to detect the referenceinterference light with the detector in the second state.

The above ophthalmic device is switched between the first state in whichthe light from the light source is emitted onto the subject eye and thesecond state in which the light from the light source is guided to thesecond reference optical system. When the subject eye is measured, themeasurement interference light is detected with the detector in thefirst state and the reference interference light is detected with thedetector in the second state. That is, the period for detecting themeasurement interference light and the period for detecting thereference interference light are different. Due to this, the referenceposition calculated from the reference interference signal can be set toa desired position irrelevant to the depthwise position information ofthe subject eye that is calculated from the measurement interferencesignal.

(First aspect) In the first ophthalmic device disclosed herein, thecontroller may be configured to control the switching unit to detect thereference interference signal with the detector in the second statebefore or after detecting the measurement interference light with thedetector in the first state. According to this configuration, thereference position is obtained before or after the depthwise positioninformation of the subject eye is obtained. Due to this, the depthwiseposition information of the subject eye can be corrected by suitablytaking into consideration the situation at the time of the measurement.

(Second aspect) In the first ophthalmic device or the first aspectdisclosed herein, the ophthalmic device may further comprise a storageunit configured to store a specific-time reference position indicatingthe reference position adjusted at a specific time, the specific-timereference position being a position calculated from the referenceinterference light generated by combining the second reference lightgenerated in the second reference optical system and the first referencelight generated in the first reference optical system at the specifictime. The controller may be configured to correct the depthwise positioninformation of the subject eye calculated based on the measurementinterference signal outputted from the detector when the subject eye ismeasured, the depthwise position information being corrected based on adifference between a measurement-time reference position and thespecific-time reference position stored in the storage unit, themeasurement-time reference position being the reference positioncalculated based on the reference interference signal outputted from thedetector when the subject eye is measured. According to thisconfiguration, the depthwise position information of the subject eye iscorrected based on the reference position obtained at the time of themeasurement and the reference position obtained at the specific time(such as, pre-shipping calibration or repair calibration). Due to this,chronological changes that may occur in the optical systems between thespecific time and the measurement can be taken into consideration.

(Third aspect) In the second aspect of the first ophthalmic devicedisclosed herein, the storage unit may be configured to further store aconversion formula for converting the depthwise position information ofthe subject eye calculated based on the measurement interference signalto an actual measurement of the subject eye, the controller may beconfigured to further calculate the actual measurement of the subjecteye by converting the depthwise position information of the subject eyecalculated based on the measurement interference signal with theconversion formula, and the conversion formula may be obtained by using(A) depthwise position information of at least two reflection surfacesof a calibration tool having a known optical path length difference and(B) the optical path length difference between the at least tworeflection surfaces, the depthwise position information of the at leasttwo reflection surfaces being obtained from calibration interferencelight generated by combining calibration measurement light and the firstreference light generated in the first reference optical system, thecalibration measurement light being generated by irradiating thecalibration tool from the measurement optical system with the light fromthe light source. According to this configuration, the actual depthwiselength of the subject eye can be calculated with high accuracy.

(Fourth aspect) In the third aspect of the first ophthalmic devicedisclosed herein, the specific time and a time at which the calibrationinterference light is measured by using the calibration tool to obtainthe conversion formula may be substantially simultaneous According tothis configuration, since the time when the specific-time referenceposition is measured and the time when the measurement is performed toobtain the conversion formula are substantially simultaneous, accuracyof the measurement of the subject eye can be improved.

(Fifth aspect) In the first ophthalmic device disclosed herein, thefirst ophthalmic device may further comprise a storage unit configuredto store a specific-time reference position indicating the referenceposition adjusted at a specific time, the specific-time referenceposition being a position calculated from the reference interferencelight generated by combining the second reference light generated in thesecond reference optical system and the first reference light generatedin the first reference optical system at the specific time. The firstreference optical system may comprise an adjuster configured to adjustan optical path length of the first reference light, and the controllermay be configured to calculate a measurement-time reference positionthat is the reference position calculated based on the referenceinterference signal outputted from the detector when the subject eye ismeasured and to control the adjuster so that the measurement-timereference position calculated when the subject eye is measured matchesthe specific-time reference position stored in the storage unit.According to this configuration, the subject eye can be measured insubstantially the same state as the state at the specific time byadjusting the optical path length of the first reference light.

(Sixth aspect) In the fifth aspect of the first ophthalmic devicedisclosed herein, the storage unit may be configured to further store aconversion formula for converting the depthwise position information ofthe subject eye calculated based on the measurement interference signalto an actual measurement of the subject eye, the controller may beconfigured to further calculate the actual measurement of the subjecteye by converting the depthwise position information of the subject eyecalculated based on the measurement interference signal with theconversion formula, and the conversion formula may be obtained by using(A) depthwise position information of at least two reflection surfacesof a calibration tool having a known optical path length difference and(B) the optical path length difference between the at least tworeflection surfaces, the depthwise position information of the at leasttwo reflection surfaces being obtained from calibration interferencelight generated by combining calibration measurement light and the firstreference light generated in the first reference optical system, thecalibration measurement light being generated by irradiating thecalibration tool from the measurement optical system with the light fromthe light source. According to this configuration, the actual depthwiselength of the subject eye can be calculated with high accuracy.

(Seventh aspect) In the sixth aspect of the first ophthalmic devicedisclosed herein, the specific time and a time at which the calibrationinterference light is measured by using the calibration tool to obtainthe conversion formula may be substantially simultaneous. According tothis configuration, since the specific time and the time at which themeasurement is performed to obtain the conversion formula aresubstantially simultaneous, the accuracy of the measurement of thesubject eye can be improved.

(Eighth aspect) In any of the fifth to seventh aspects of the firstophthalmic device disclosed herein, the controller may be configured to:detect the reference interference light with the detector while theswitching unit is in the second state; control the adjuster so that themeasurement-time reference position calculated based on the referenceinterference signal outputted from the detector matches thespecific-time reference position stored in the storage unit; and detectthe measurement interference light while the switching unit is in thefirst state after the optical path length of the first reference lightis adjusted by the adjuster. According to this configuration, thesubject eye is measured after the optical path length of the firstreference light is adjusted to be in the same state as the specifictime. Due to this, the subject eye can be measured under the sameconditions as those of the specific time (such as pre-shippingcalibration or repair calibration).

A second ophthalmic device disclosed herein may comprise: a first OCTconfigured to measure a first depthwise position of a first part of asubject eye; a second OCT configured to measure a second depthwiseposition of a second part of the subject eye, the second part beingdifferent from the first part; and a controller configured to calculatea depthwise length from the first part to the second part based on thefirst depthwise position measured by the first OCT and the seconddepthwise position measured by the second OCT. The first OCT maycomprise: a first light source; a first measurement optical systemconfigured to generate first measurement light by irradiating the firstpart of the subject eye with light from the first light source; a firstreference optical system configured to generate first reference light byusing the light from the first light source; a second reference opticalsystem configured to generate second reference light by using the lightfrom the first light source, the second reference light being used forcalculating a first reference position; a first interference opticalsystem configured to generate first measurement interference light bycombining the first measurement light and the first reference light andto generate first reference interference light by combining the secondreference light and the first reference light; and a first detectorconfigured to detect the first measurement interference light and outputa first measurement interference signal and to detect the firstreference interference light and output a first reference interferencesignal. The second reference optical system may include an optical pathbranching from the first measurement optical system, the firstmeasurement optical system my comprise a first switching unit configuredto switch between a first state and a second state, the first statebeing a state in which the subject eye is irradiated with the light fromthe first light source and the second state being a state in which thelight from the first light source is guided to the second referenceoptical system, and when the subject eye is measured, the first detectormay be configured to detect the first measurement interference lightwhile the first switching unit is in the first state, and to detect thefirst reference interference light while the first switching unit is inthe second state.

With the above ophthalmic device as well, the first measurementinterference light is detected while the first detector is in the firststate and the first reference interference light is detected while thefirst detector is in the second state. Due to this, the first referenceposition calculated from the first reference interference signal can beset to a desired position irrelevant to the depthwise positioninformation of the subject eye that is calculated from the firstmeasurement interference signal.

(Ninth aspect) In the second ophthalmic device disclosed herein, thesecond OCT may comprise: a second light source; a second measurementoptical system configured to generate second measurement light byirradiating the second part of the subject eye with light from thesecond light source; a third reference optical system configured togenerate third reference light by using the light from the second lightsource; a fourth reference optical system configured to generate fourthreference light by using the light from the second light source, thefourth reference light being used for calculating a second referenceposition; a second interference optical system configured to generatesecond measurement interference light by combining the secondmeasurement light and the third reference light and to generate secondreference interference light by combining the fourth reference light andthe third reference light; and a second detector configured to detectthe second measurement interference light and output a secondmeasurement interference signal and to detect the second referenceinterference light and output a second reference interference signal.The fourth reference optical system may include an optical pathbranching from the second measurement optical system, the secondmeasurement optical system may comprise a second switching unitconfigured to switch between a third state and a fourth state, the thirdstate being a state in which the subject eye is irradiated with thelight from the second light source and the fourth state being a state inwhich the light from the second light source is guided to the fourthreference optical system, and when the subject eye is measured, thesecond detector may be configured to detect the second measurementinterference light while the second switching unit is in the thirdstate, and to detect the second reference interference light while thesecond switching unit is in the fourth state. According to thisconfiguration, similar to the first OCT, the second reference positioncan be set to a desired position with the second OCT.

(Tenth aspect) In the ninth aspect of the second ophthalmic devicedisclosed herein, when the first switching unit is switched to the firststate, the second switching unit may be switched to the third state,when the first switching unit is switched to the second state, thesecond switching unit may be switched to the fourth state, and the firstswitching unit and the second switching unit may be a single switchingunit shared by the first measurement optical system and the secondmeasurement optical system. According to this configuration, since thefirst switching unit and the second switching unit are a singleswitching unit shared by the first measurement optical system and thesecond measurement optical system, the configuration of the opticalsystem can be simplified and the switch performed by each of theswitching unit can be facilitated.

(Eleventh aspect) In the ninth or tenth aspect of the second ophthalmicdevice disclosed herein, the ophthalmic device may further comprise astorage unit configured to store a depthwise distance between ameasurement area of the first OCT and a measurement area of the secondOCT adjusted at a specific time, a first specific-time referenceposition indicating the first reference position adjusted at thespecific time, and a second specific-time reference position indicatingthe second reference position adjusted at the specific time. Thecontroller may be configured to calculate the depthwise length from thefirst part to the second part based on: (1) a difference between a firstmeasurement-time reference position and the first specific-timereference position stored in the storage unit, the firstmeasurement-time reference position being calculated based on the firstreference interference signal outputted from the first detector when thesubject eye is measured; (2) the first position of the subject eyecalculated based on the first measurement interference signal outputtedfrom the first detector when the subject eye is measured; (3) adifference between a second measurement-time reference position and thesecond specific-time reference position stored in the storage unit, thesecond measurement-time reference position being calculated based on thesecond reference interference signal outputted from the second detectorwhen the subject eye is measured; (4) the second position of the subjecteye calculated based on the second measurement interference signaloutputted from the second detector when the subject eye is measured; and(5) the depthwise distance between the measurement area of the first OCTand the measurement area of the second OCT stored in the storage unit.According to this configuration, the depthwise length between the firstpart and the second part can be calculated with high accuracy.

(Twelfth aspect) In the eleventh aspect of the second ophthalmic devicedisclosed herein, the storage unit may be configured to further store: afirst conversion formula for converting depthwise position informationof the subject eye calculated based on the first measurementinterference signal to an actual measurement of the subject eye in themeasurement area of the first OCT; and a second conversion formula forconverting depthwise position information of the subject eye calculatedbased on the second measurement interference signal to an actualmeasurement of the subject eye in the measurement area of the secondOCT. The controller may be configured to further calculate the actualmeasurement of the subject eye in the measurement area of the first OCTby converting the depthwise position information of the subject eyecalculated based on the first measurement interference signal with thefirst conversion formula, and to further calculate the actualmeasurement of the subject eye in the measurement area of the second OCTby converting the depthwise position information of the subject eyecalculated based on the second measurement interference signal with thesecond conversion formula. The first conversion formula may be obtainedby using (A1) depthwise position information of at least two reflectedsurfaces of a first calibration tool having a known an optical pathlength difference and (B1) the optical path length difference betweenthe at least two reflected surfaces, the depthwise position informationof the at least two reflected surfaces of the first calibration tool isobtained from first calibration interference light generated bycombining first calibration measurement light and first reference lightgenerated in the first reference optical system, the first calibrationmeasurement light being generated by irradiating the first calibrationtool from the first measurement optical system with the light from thefirst light source. The second conversion formula may be obtained byusing (A2) depthwise position information of at least two reflectedsurfaces of a second calibration tool having a known optical path lengthdifference and (B2) the optical path length difference between the atleast two reflected surfaces, the depthwise position information of theat least two reflected surfaces of the second calibration tool isobtained from second calibration interference light generated bycombining second calibration measurement light and third reference lightgenerated in the third reference optical system, the second calibrationmeasurement light is generated by irradiating the second calibrationtool from the second measurement optical system with the light from thesecond light source. According to this configuration, the actualdepthwise length of the subject eye can be calculated with highaccuracy.

(Thirteenth aspect) In the twelfth aspect of the second ophthalmicdevice disclosed herein, the first specific-time reference position maybe a position calculated from the first reference interference lightgenerated by combining the second reference light generated in thesecond reference optical system and the first reference light generatedin the first reference optical system at the specific time. The secondspecific-time reference position may be a position calculated from thesecond reference interference light generated by combining the fourthreference light generated in the fourth reference optical system and thethird reference light generated in the third reference optical system atthe specific time. The specific time, a time at which the firstcalibration tool is irradiated with the first measurement light toobtain the first conversion formula and a time at which the secondcalibration tool is irradiated to the second measurement light to obtainthe second conversion formula may be substantially simultaneous.According to this configuration, since the specific time and the time atwhich the measurement is performed to obtain the conversion formula aresubstantially simultaneous, the accuracy of the measurement of thesubject eye can be improved.

(Fourteenth aspect) In the ninth or tenth aspect of the secondophthalmic device disclosed herein, the ophthalmic device may furthercomprise an adjuster disposed on at least one of the first referenceoptical system and the third reference optical system and configured toadjust an optical path length of the at least one of the first referenceoptical system and the third reference optical system. The controllermay be configured to control the adjuster so that a distance between afirst measurement-time reference position calculated from the firstreference interference signal when the subject eye is measured and asecond measurement-time reference position calculated from the secondreference interference signal when the subject eye is measured matches apredetermined distance. According to this configuration, the subject eyeis measured after the relationship of the optical path lengths of thefirst and third reference optical systems is adjusted to thepredetermined distance. Due to this, the depthwise length between thefirst part and the second part of the subject eye can be calculated withhigh accuracy.

(Fifteenth aspect) in the fourteenth aspect of the second ophthalmicdevice disclosed herein, the predetermined distance may be a distancebetween a first specific-time reference position calculated from thefirst reference interference signal at a specific time and a secondspecific-time reference position calculated from the second referenceinterference signal at the specific time. According to thisconfiguration, the subject eye can be measured under the same conditionsas those of the specific time (such as pre-shipping calibration orrepair calibration).

(Sixteenth aspect) In the fourteenth or fifteenth aspect of the secondophthalmic device disclosed herein, the controller may be configured to:detect the first reference interference light with the first detectorwhile the first switching unit is in the second state; detect the secondreference interference light with the second detector while the secondswitching unit is the fourth state; control the adjuster so that adifference between the first measurement-time reference positioncalculated based on the first reference interference signal outputtedfrom the first detector and the second measurement-time referenceposition calculated based on the second reference interference signaloutputted from the second detector matches the predetermined distance,and after the optical path length is adjusted by the adjuster, detectthe first measurement interference signal while the first switching unitis in the first state, and detect the second measurement interferencesignal while the second switching unit is in the third state.

EMBODIMENTS First Embodiment

An ophthalmic device 10 according to a first embodiment will bedescribed. The ophthalmic device 10 comprises an anterior part OCT (anexample of “first OCT”) configured to capture tomographic images of ananterior part of a subject eye (example of “first part”) and a retinaOCT (an example of “second OCT”) configured to capture tomographicimages of a retina of the subject eye (an example of “second part”). Theophthalmic device 10 enables to obtain a clear tomographic image of eachof the anterior part and the retina by capturing the tomographic imagesusing different OCTs for the anterior part and the retina.

That is, as shown in FIG. 2 , the ophthalmic device 10 captures atomographic image of an anterior part 202 of a subject eye 200 using theanterior part OCT and a tomographic image of a retina 204 using theretina OCT. In order to clearly capture each of the anterior part 202and the retina 204, an imaging range 202 a (depthwise length B) of theanterior part OCT and an imaging range 204 a (depthwise length C) of theretina OCT are set so that they do not overlap. Due to this, when anaxial length (length from a corneal surface of the anterior part 202 (anexample of “first position”) to a retinal surface of the retina 204 (anexample of “second position”)) is to be measured, for example, adepthwise positional relationship between the imaging range 202 a of theanterior part OCT and the imaging range 204 a of the retina OCT needs tobe identified in advance. For example, a distance (length A) from arearmost position in the imaging range 202 a of the anterior part OCT toa frontmost position of the imaging range 204 a of the retina OCT isrequired. Thus, the configuration of the optical systems of theophthalmic device 10 is designed and calibration of the optical systemsof the ophthalmic device 10 is performed when the ophthalmic device 10is shipped so that the depthwise positional relationship between theimaging range 202 a of the anterior part OCT and the imaging range 204 aof the retina OCT satisfies a predetermined positional relationship.However, the optical systems of the ophthalmic device 10 undergo changessuch as post-shipment chronological changes and those caused byenvironment (such as temperature) upon the measurement, thus measurementunder the condition calibrated in a calibration process cannot beachieved. Due to this, the ophthalmic device 10 is configured tocalculate the axial length by correcting change(s) in optical pathlengths of the optical systems.

Firstly, the configuration of the optical systems of the ophthalmicdevice 10 will be described. As shown in FIG. 1 , the ophthalmic device10 includes the anterior part OCT (12, 18 a to 18 e, 20, 22, 26, 24, 28,34, 36, 38, 40, 43) and the retina OCT (14, 16, 30 a to 30 d, 32, 33,36, 38, 41, 42).

The anterior part OCT is a Fourier domain optical coherence tomographicdevice (so-called SS-OCT) comprising a wavelength sweeping light source12 (an example of “first light source”), an anterior part measurementoptical system (an example of “first measurement optical system”), afirst anterior part reference optical system (an example of “firstreference optical system”), a second anterior part reference opticalsystem (an example of “second reference optical system”), an anteriorpart interference optical system (an example of “first interferenceoptical system”), and an anterior part detector 28 (an example of “firstdetector”).

The anterior part measurement optical system comprises optical fibers 18a, 18 b, 18 d, a coupler 20, a circulator 22, a lens 34, and a Galvanoscanner 36. Light emitted from the light source 12 is inputted to thecoupler 20 through the optical fiber 18 a. The coupler 20 is configuredto split the light from the light source 12 into measurement light andfirst reference light. The measurement light (an example of “firstmeasurement light”) split by the coupler 20 is outputted to the opticalfiber 18 b. The circulator 22 is arranged on the optical fiber 18 b. Themeasurement light outputted to the optical fiber 18 b travels throughthe circulator 22 and is outputted toward the lens 34 from the end ofthe optical fiber 18 b. The measurement light outputted to the lens 34is further outputted to the 2-axis Galvano scanner 36. The Galvanoscanner 36 is configured to be tilted by a driving device that is notshown, and a position at which the measurement light is emitted to thesubject eye 200 is scanned by tilting the Galvano scanner 36. Reflectedlight from the subject eye 200 is inputted to the lens 34 via theGalvano scanner 36 in a reversed direction from the aforementioneddirection. The reflected light inputted to the lens 34 travels throughthe optical fiber 18 b and is inputted to the circulator 22. Thereflected light inputted to the circulator 22 travels through theoptical fiber 18 d and is inputted to a coupler 26. In FIG. 1 , theconfiguration of the optical systems has been simplified, thus theoptical fiber 18 b is depicted as if it is penetrating through a lens33, however, the optical fiber 18 b actually does not penetrate throughthe lens 33. Further, in FIG. 1 , the circulator 22 is depicted as if itis arranged on an optical fiber 30 c to be described later, however, thecirculator 22 is actually not arranged on the optical fiber 30 c.

The first anterior part reference optical system comprises opticalfibers 18 a, 18 c, 18 e, the coupler 20, a circulator 24, a lens 43, anda reference mirror 40. As aforementioned, the light emitted from thelight source 12 is inputted to the coupler 20 through the optical fiber18 a, and is split into the measurement light and the first referencelight in the coupler 20. The first reference light outputted from thecoupler 20 (an example of “first reference light”) is inputted to theoptical fiber 18 c, travels through the circulator 24, and is outputtedtoward the lens 43 from the end of the optical fiber 18 c. The firstreference light outputted to the lens 43 is reflected on the referencemirror 40, and is then inputted again into the lens 43. The reflectedlight inputted to the lens 43 travels through the optical fiber 18 c andis inputted to the circulator 24. The reflected light inputted to thecirculator 24 is inputted to the coupler 26 through the optical fiber 18e.

The second anterior part reference optical system comprises an opticalpath that branches from the anterior part measurement optical system andcomprises a reference mirror 38 arranged on this optical path. Theaforementioned Galvano scanner 36 is tilted by the driving device thatis not shown, by which it switches between a first state in which thelight from the light source 12 is emitted to the subject eye 200 and asecond state in which the light from the light source 12 is emitted tothe reference mirror 38. The Galvano scanner 36 functions as a “firstswitching unit” configured to switch between the first state and thesecond state. Further, in the present embodiment, in the state where thelight from the light source 12 is emitted onto the subject eye 200, thelight from the light source 12 is not guided to the reference mirror 38.On the other hand, in the state where the light from the light source 12is guided to the reference mirror 38, the light from the light source 12is not emitted onto the subject eye 200. That is, an entirety of thelight guided from the light source 12 to the anterior part measurementoptical system is emitted to the subject eye 200 or to the referencemirror 38. The light emitted to the reference mirror 38 (an example of“second reference light”) is reflected on the reference mirror 38 and isinputted to the circulator 22 through the Galvano scanner 36, the lens34, and the optical fiber 18 b. The light inputted to the circulator 22is inputted to the coupler 26 through the optical fiber 18 d.

The anterior part interference optical system comprises the coupler 26.The coupler 26 is configured to combine the light reflected from thesubject eye 200 (first measurement light) and the light reflected fromthe reference mirror 40 (first reference light) and generateinterference light (an example of “first measurement interferencelight”), and to combine the light reflected from the reference mirror 38(second reference light) and the light reflected from the referencemirror 40 (first reference light) and generate interference light (anexample of “first reference interference light”). The interference lightgenerated in the coupler 26 is inputted to the anterior part detector28. The anterior part detector 28 is a balance detector and isconfigured to detect the interference light inputted from the coupler 26and output an interference signal (electric signal). The interferencesignal outputted from the anterior part detector 28 is inputted to acontroller 44 (shown in FIG. 3 ) described later.

The retina OCT is a spectrum domain optical coherence tomographic device(so-called SD-OCT) comprising a wide-band wavelength light source 14 (anexample of “second light source”), and comprises a retina measurementoptical system (an example of“second measurement optical system”), afirst retina reference optical system (an example of “third referenceoptical system”), a second retina reference optical system (an exampleof “fourth reference optical system”), a retina interference opticalsystem (an example of“second interference optical system”), and a retinadetector 16 (an example of “second detector”).

The retina measurement optical system comprises optical fibers 30 a, 30c, a coupler 32, the lens 33, and the Galvano scanner 36. Lightoutputted from the light source 14 is inputted to the coupler 32 throughthe optical fiber 30 a. The coupler 32 is configured to split the lightfrom the light source 14 into measurement light (an example of “secondmeasurement light”) and third reference light. The measurement lightsplit by the coupler 32 is outputted to the optical fiber 30 c and isoutputted toward the lens 33 from the end of the optical fiber 30 c.Similar to the anterior part OCT described above, the measurement lightoutputted to the lens 33 is outputted to the 2-axis Galvano scanner 36.The Galvano scanner 36 is driven by the driving device that is notshown, and a position at which the measurement light is emitted to thesubject eye 200 is scanned. Reflected light from the subject eye 200 isinputted to the coupler 32 through the Galvano scanner 36, the lens 33,and the optical fiber 30 c in a reversed direction from theaforementioned direction.

As it is apparent from the foregoing description, the optical path fromthe Galvano scanner 36 to the subject eye 200 is shared by the retinameasurement optical system and the anterior part measurement opticalsystem, and the Galvano scanner 36 is shared by the retina measurementoptical system and the anterior part measurement optical system. In FIG.1 , the measurement light outputted from the end of the optical fiber 30c toward the lens 33 is depicted as if it penetrates through the lens34, however, it actually does not penetrate through the lens 34.Further, as shown in FIG. 1 , an optical path length from the end of theoptical fiber 30 c to the subject eye 200 in the retina measurementoptical system is longer than an optical path length from the end of theoptical fiber 18 b to the subject eye 200 in the anterior partmeasurement optical system. That is, a portion between positionscorresponding to the end of the optical fiber 30 c and the end of theoptical fiber 18 b is configured by a bulk optical system in the retinameasurement optical system, whereas the portion is configured with theoptical fiber 18 b in the anterior part measurement optical system. Dueto this, a change in the optical path length of the anterior partmeasurement optical system and a change in the optical path length ofthe retina measurement optical system caused by a temperature change donot become identical to one another. Further, since a temperature in theophthalmic device 10 is not uniform, a temperature of each of theoptical systems does not become uniform over its entire optical pathlength. Due to these factors as well, the changes in the optical pathlengths of the respective optical systems caused by a temperature arenonuniform.

The first retina reference optical system comprises optical fibers 30 a,30 b, the coupler 32, a lens 41, and a reference mirror 42. As describedabove, the light emitted from the light source 14 is inputted to thecoupler 32 through the optical fiber 30 a and is split in the coupler 32into measurement light and third reference light. The reference lightoutputted from the coupler 32 (an example of “third reference light”)travels through the optical fiber 30 b and is outputted from the end ofthe optical fiber 30 b toward the lens 41. The third reference lightoutputted to the lens 41 is reflected on the reference mirror 42, and isinputted to the coupler 32 through the lens 41 and the optical fiber 30b.

The second retina reference optical system comprises an optical paththat branches from the retina measurement optical system, and comprisesthe reference mirror 38 arranged on this optical path. As it is apparentfrom FIG. 1 , the reference mirror 38 is shared by the second retinareference optical system and the second anterior part reference opticalsystem, and the second retina reference optical system has identicalconfiguration as the second anterior part reference optical system.Thus, the Galvano scanner 36 is driven to switch between a third statein which the light from the light source 14 is emitted to the subjecteye 200 and a fourth state in which the light from the light source 14is emitted to the reference mirror 38. That is, the Galvano scanner 36functions as a “second switching unit” configured to switch between thethird state and the fourth state. As it will be described later, sincethe anterior part OCT and the retina OCT capture the tomographic imagesof the subject eye 200 simultaneously, the retina OCT is switched to thethird state when the Galvano scanner 36 switches the anterior part OCTto the first state. Further, when the Galvano scanner 36 switches theanterior part OCT to the second state, the retina OCT is switched to thefourth state. In the retina OCT as well, an entirety of the light guidedfrom the light source 14 to the retina measurement optical system isemitted to the subject eye 200 or to the reference mirror 38. The lightemitted to the reference mirror 38 (an example of“fourth referencelight”) is reflected on the reference mirror 38 and is inputted to thecoupler 32 through the Galvano scanner 36 and the optical fiber 30 c.

The retina interference optical system comprises the coupler 32. Thecoupler 32 is configured to combine the light reflected from the subjecteye 200 (second measurement light) and the light reflected from thereference mirror 42 (third reference light) and generate interferencelight (an example of “second measurement interference light”), and tocombine the light reflected from the reference mirror 38 (fourthreference light) and the light reflected from the reference mirror 42(third reference light) and generate interference light (an example of“second reference interference light”). The interference light generatedin the coupler 32 is inputted to the retina detector 16. The retinadetector 16 is a splitter and is configured to split and detect theinputted interference light and output an interference signal (electricsignal). The interference signal outputted from the retina detector 16(spectrum information of the interference light) is inputted to thecontroller 44 (shown in FIG. 3 ) described later.

Next, the controlling configuration of the ophthalmic device 10 will bedescribed. As shown in FIG. 3 , the ophthalmic device 10 is controlledby the controller 44. The controller 44 is configured of a microcomputer(microprocessor) configured of, for example, a CPU, a ROM, and a RAM,and functions as a computing unit 46 configured to calculate the axiallength of the subject eye 200 and a storage unit 48 configured to storevarious types of information. The controller 44 has the light sources12, 14, the anterior part detector 28, the retina detector 16, and theGalvano scanner 36 connected thereto. The controller 44 is configured tocontrol on/off of the light sources 12, 14 and drive the Galvano scanner36. Further, the controller 44 is configured to generate tomographicimages of the anterior part 202 of the subject eye 200 using theinterference signals inputted from the anterior part detector 28 andgenerate tomographic images of the retina 204 of the subject eye 200using the interference signals inputted from the retina detector 16. Thetomographic images generated by the controller 44 are displayed on amonitor that is not shown.

Further, the computing unit 46 of the controller 44 is configured tocalculate the axial length of the subject eye 200 (length from theanterior surface of the cornea to the retinal surface of the subject eye200) based on the interference signal inputted from the anterior partdetector 28 (depthwise position information of the anterior part 202 a)and the interference signal inputted from the retina detector 16(depthwise position information of the retina 204). As aforementioned,in order to calculate the axial length of the subject eye 200, thedepthwise positional relationship between the imaging range 202 a of theanterior part OCT and the imaging range 204 a of the retina OCT (such asthe distance (length A) from the rearmost position in the imaging range202 a of the anterior part OCT to the frontmost position of the imagingrange 204 a of the retina OCT) is required. Thus, the storage unit 48 ofthe controller 44 stores the depthwise positional relationship (lengthA) of the imaging range 202 a of the anterior part OCT and the imagingrange 204 a of the retina OCT at the time of shipping of the ophthalmicdevice 10. More specifically, a conversion formula (an example of “firstconversion formula”) for converting the depthwise position informationof the subject eye 200 calculated from the interference signals measuredby the anterior part OCT to an actual measurement of the subject eye anda conversion formula (an example of “second conversion formula”) forconverting the depthwise position information of the subject eye 200calculated form the interference signals measured by the retina OCT tothe actual measurement of the subject eye are stored, and further, thedepthwise positional relationship of the imaging range 202 a of theanterior part OCT and the imaging range 204 a of the retina OCT (such asthe length A) at the time of shipment of the ophthalmic device 10 isstored. These conversion formulas and the positional relationships areobtained upon performing the calibration process of the optical systemsthat is performed at the time of shipment of the ophthalmic device 10.

Even if the optical systems of the ophthalmic device 10 are calibratedupon the shipping and the depthwise positional relationship (conversionformula (length A)) of the imaging range 202 a and the imaging range 204a at the time of shipping is stored, the optical path lengths of theoptical systems change by post-shipping chronological changes and theenvironment (such as temperature) at the time of measurement. As aresult, the depthwise positional relationship of the imaging range 202 aand the imaging range 204 a changes, and with the depthwise positionalrelationship changed, the axial length cannot be calculated correctly.Thus, in the present embodiment, the storage unit 48 of the controller44 further stores a position of the reference mirror 38 in the anteriorpart OCT at the time of shipping (an example of “first specific-timereference position”) and a position of the reference mirror 38 in theretina OCT at the time of shipping (an example of “second specific-timereference position”).

Here, examples of the calibration process of the optical systemsperformed at the time of shipment of the ophthalmic device 10 and aprocess for obtaining the conversion formulas for calculating the axiallength will be described. When the calibration process of the opticalsystems is to be performed, a calibration tool (glass block) having atleast two reflection surfaces having a known optical path lengthdifference is used. That is, front and rear surfaces of the glass blockserve as reflection surfaces, and a length from the front surface to therear surface (thickness of the glass block) is known. Due to this, theglass block can be used as the calibration tool.

As specific processes, the calibration tool (glass block) is positionedat the position of the anterior part of the subject eye 200, thecalibration tool is measured by the anterior part OCT, and the positionof the front surface and the position of the rear surface of thecalibration tool are obtained. As aforementioned, since the optical pathlength difference between the position of the front surface and theposition of the rear surface of the calibration tool is known, theconversion formula (first conversion formula) for converting the valuemeasured by the anterior part OCT to the actual length is therebyobtained. Similarly, the calibration tool (glass block) is positioned atthe position of the retina of the subject eye 200, the calibration toolis measured by the retina OCT, and the position of the front surface andthe position of the rear surface of the calibration tool are obtained.Due to this, the conversion formula (second conversion formula) forconverting the value measured by the retina OCT to the actual length isthereby obtained. Then, the calibration tool is arranged so that thefront surface of the calibration tool is positioned in the imaging range202 a of the anterior part OCT and the rear surface of the calibrationtool is positioned in the imaging range 204 a of the retina OCT, theposition of the front surface of the calibration tool is obtained by theanterior part OCT, and the position of the rear surface of thecalibration tool is obtained by the retina OCT. Due to this, thepositional relationship (such as the length A) of the imaging range 202a of the anterior part OCT and the imaging range 204 a of the retina OCTcan be obtained. The conversion formulas for calculating the axiallength of the subject eye 200 (actual length thereof) are obtained bythese measurements, and the obtained conversion formulas are stored inthe storage unit 48.

At the same time as obtaining the aforementioned conversion formulas,the position of the reference mirror 38 in the anterior part OCT and theposition of the reference mirror 38 in the retina OCT are measured. Thatis, upon measuring the calibration tool using the anterior part OCT, theGalvano scanner 36 is driven after this measurement is completed and thelight from the light source 12 is emitted to the reference mirror 38.Then, the position of the reference mirror 38 in the anterior part OCTis obtained from reference interference light obtained by combing thesecond reference light reflected on the reference mirror 38 and thefirst reference light. Similarly, upon measuring the calibration toolusing the retina OCT, the Galvano scanner 36 is driven after thismeasurement is completed and the light from the light source 14 isemitted to the reference mirror 38. Then, the position of the referencemirror 38 in the retina OCT is obtained from reference interferencelight obtained by combing the fourth reference light reflected on thereference mirror 38 and the third reference light. Then, these tworeference positions are stored in the storage unit 48. By storing theconversion formulas and the reference positions in the storage unit 48,the calibration process at the time of shipment of the ophthalmic device10 is completed. The calibration process as above may be performed notonly at the time of shipment of the ophthalmic device 10 but at variousother timings. For example, it may be performed at the time of repairingor maintenance of the ophthalmic device 10. Further, in the aboveexample, the process to measure the reference positions was performedafter the measurement for obtaining the conversion formulas wasperformed, however, the measurement process for obtaining the conversionformulas may be performed after the process to measure the referencepositions was performed.

Next, the operation of the ophthalmic device 10 for measuring the axiallength of the subject eye 200 after the shipment will be described. Inorder to measure the axial length of the subject eye 200, firstly theoptical systems of the anterior part OCT and the retina OCT arepositioned (aligned) relative to the subject eye 200. Then, thecontroller 44 turns on the light sources 12, 14 as shown in FIG. 4(S10). By doing so, the light is outputted from each of the lightsources 12, 14, and the outputted light is emitted onto the subject eye200. That is, the light outputted from both the light sources 12, 14 isemitted simultaneously to the subject eye 200.

Then, the controller 44 captures tomographic images of the anterior part202 and the retina 204 of the subject eye 200 (S12). Specifically, thecontroller 44 drives the Galvano scanner 36 and scans the light from thelight sources 12, 14 to the measurement areas of the subject eye 200.Due to this, the interference light obtained from the light reflected onthe anterior part 202 of the subject eye 200 is detected by the anteriorpart detector 28, and at the same time the interference light obtainedfrom the light reflected on the retina 204 of the subject eye 200 isdetected by the retina detector 16. Due to this, the controller 44generates the tomographic image of the anterior part 202 of the subjecteye 200 based on the interference signal inputted from the anterior partdetector 28 and generates the tomographic image of the retina 204 of thesubject eye 200 based on the interference signal inputted from theretina detector 16.

Next, the controller 44 emits the light from the light sources 12, 14 tothe reference mirror 38 and measures the position of the referencemirror 38 (S14). Specifically, the controller 44 drives the Galvanoscanner 36 to guide the light from the light sources 12, 14 to thesecond reference optical system, and emits the light from the lightsources 12, 14 to the reference mirror 38. As aforementioned, in thestate of S14, the light from the light sources 12, 14 is not emitted tothe subject eye 200. Due to this, the anterior part detector 28 detectsonly the interference light obtained from the light emitted to thereference mirror 38 (second reference light) and the first referencelight, and the retina detector 16 detects only the interference lightobtained from the light emitted to the reference mirror 38 (fourthreference light) and the third reference light. Based on the detectedinterference light as above, the controller 44 calculates the positionof the reference mirror 38 in the anterior part OCT and the position ofthe reference mirror 38 in the retina OCT.

Next, the controller 44 calculates the axial length of the subject eye200 based on the measurement result of the subject eye 200 as measuredin S12 and the measurement result of the reference mirror 38 as measuredin S14 (S16). That is, in S12, the tomographic image of the anteriorpart 202 of the subject eye 200 is captured by the anterior part OCT andthe tomographic image of the retina 204 of the subject eye 200 iscaptured by the retina OCT. Thus, the controller 44 can identify theposition of the corneal surface of the subject eye 200 from thetomographic image of the anterior part 202 and the position of theretinal surface of the subject eye 200 from the tomographic image of theretina 204. Here, the storage unit 48 of the controller 44 stores thepositional relationship (length A) of the imaging range 202 a of theanterior part OCT and the imaging range 204 a of the retina OCT as wellas the conversion formulas. Thus, if there is no change in the opticalpath lengths of the optical systems in the anterior part OCT and theretina OCT, the controller 44 can calculate the axial length from theidentified positions of the corneal surface and the retinal surface, theconversion formulas (length A), and the positional relationship.

However, as already explained, the optical path lengths of the opticalsystems of the ophthalmic device 10 change due to the post-shippingchronological changes and the environment (such as temperature) at thetime of measurement. Due to this, the controller 44 uses the position ofthe reference mirror 38 calculated in S14 to correct the position of thecorneal surface and the position of the retinal surface identified fromthe tomographic images captured in S12. That is, the storage unit 48 ofthe controller 44 stores the position of the reference mirror 38 in theanterior part OCT at the time of shipping and the position of thereference mirror 38 in the retina OCT at the time of shipping. Thus, ineach of the anterior part OCT and the retina OCT, a difference betweenthe position of the reference mirror 38 measured in S14 and a positionof the reference mirror 38 as stored in the storage unit 48 (that is,the change in the optical path length) is used to correct the positionsof the corneal surface and the retinal surface identified from thetomographic images captured in S12. Next, the axial length is calculatedfrom the corrected positions of the corneal surface and the retinalsurface and the positional relationship (length A) of the imaging range202 a and the imaging range 204 a. Due to this, the axial length of thesubject eye 200 can be calculated with high accuracy. The axial lengthcalculated in S16 is displayed in the monitor that is not shown.

In the ophthalmic device 10 of the first embodiment as described above,the anterior part OCT and the retina OCT each comprise the referenceoptical system, and the reference positions (position of the referencemirror 38) measured by the reference optical systems are used to correctthe measurement results of the anterior part OCT and the retina OCT. Dueto this, even if the optical path length of the optical system of theophthalmic device 10 is changed over time or by temperature, themeasurement results of the anterior part OCT and the retina OCT arecorrected with consideration to the changes in the optical path lengths.Due to this, the axial length of the subject eye 200 can be calculatedwith high accuracy.

Further, the reference mirror 38 is irradiated with the light to measurethe position of the reference mirror 38 (reference position) after thesubject eye 200 is measured by emitting the light to the subject eye200. That is, the measurement of the subject eye 200 and the measurementof the reference mirror 38 are not performed simultaneously. Due tothis, the reference mirror 38 can be set to a desired position, and noissue arises even if position(s) of part(s) of the subject eye 200 (suchas the cornea, crystalline lens, and retina) and the position of thereference mirror 38 are at the same position. Further, the measurementof the subject eye 200 and the measurement of the reference mirror 38are not performed simultaneously, but the measurement of the referencemirror 38 is performed immediately after the measurement of the subjecteye 200 is performed. Due to this, accuracy of calculation of the axiallength is hardly affected. In the above example, the measurement of thereference mirror 38 is performed immediately after the measurement ofthe subject eye 200 is performed, however to the contrary, themeasurement of the subject eye 200 may be performed immediately afterthe measurement of the reference mirror 38 is performed.

Second Embodiment

Next, an ophthalmic device 50 according to the second embodiment will bedescribed. The ophthalmic device 50 according to the second embodimentcomprises an anterior part OCT and a retina OCT, and each of these OCTscomprises a reference optical system for obtaining a reference position,and in this point, the ophthalmic device 50 is similar to the ophthalmicdevice 10 according to the first embodiment. However, the configurationof the reference optical systems of the ophthalmic device 50 accordingto the second embodiment is different, and the configuration forcorrecting the changes in the optical path lengths of the opticalsystems of the ophthalmic device 50 based on the reference positionsobtained by the reference optical systems differs from that of theophthalmic device 10 of the first embodiment. Hereinbelow, portions ofthe configuration of the ophthalmic device 50 of the second embodimentthat are identical to that of the ophthalmic device 10 of the firstembodiment will be explained briefly, and portions with differentconfigurations from those of the first embodiment will be explained indetail.

As shown in FIGS. 5 to 7 , the ophthalmic device 10 comprises ananterior part OCT 53 (another example of “first OCT”) configured tocapture tomographic images of the anterior part of the subject eye and aretina OCT 52 (another example of “second OCT”) configured to capturetomographic images of the retina of the subject eye. The anterior partOCT 53 is an optical coherence tomographic device (SS-OCT) comprising awavelength sweeping light source 82, and comprises an anterior partmeasurement optical system (86 a, 86 c, 59, 60, 62, 63, 76, 68), a firstanterior part reference optical system (86 a, 86 d, 88, 94, 90, 96, 92),a second anterior part reference optical system (80, 74), an anteriorpart interference optical system 88, and an anterior part detector 84.

The anterior part measurement optical system comprises optical fibers 86a, 86 c, a coupler 88, a lens 59, a beam splitter 60, a Galvano scanner62, a mirror 63, a lens 76, and a mirror 68. Light outputted from thelight source 82 travels through the optical fiber 86 a and is split intomeasurement light and first reference light in the coupler 88, and themeasurement light split in the coupler 88 is outputted from the end ofthe optical fiber 86 c toward the lens 59. The measurement lightoutputted to the lens 59 is emitted to the subject eye 200 (FIG. 7 ) viathe beam splitter 60, the Galvano scanner 62, the mirror 63, the lens76, and the mirror 68. In FIG. 5 , a calibration tool 72 (such as asimulated eye) that is used as a substitute to the subject eye 200 atthe time of product shipment is shown. The calibration tool 72 has asheet of glass block at the position of the cornea and a sheet of glassblock at the position of the retina. A thickness of each glass block(optical path length difference) and a distance between the two sheetsof glass block (optical path length difference) are known. In the secondembodiment as well, the Galvano scanner 62 is driven to scan the lightemitted to the subject eye 200. The light reflected on the subject eyetravels on the aforementioned path in an opposite direction and isinputted to the coupler 88.

The first anterior part reference optical system comprises opticalfibers 86 a, 86 d, the coupler 88, a lens 94, a beam splitter 90, a lens96, and a reference mirror 92. First reference light split by thecoupler 88 is outputted from the end of the optical fiber 86 d towardthe lens 94, and is emitted to the reference mirror 92 via the beamsplitter 90 and the lens %. Light reflected on the reference mirror 92travels on the aforementioned path in an opposite direction and isinputted to the coupler 88.

The second anterior part reference optical system comprises an opticalpath branching from the anterior part measurement optical system (morespecifically, a Galvano scanner 62), and comprises a lens 80 and areference mirror 74 arranged on this optical path. The reference mirror74 has the same configuration as the calibration tool 72 used at thetime of product shipment, and is arranged such that an optical pathlength from the Galvano scanner 62 to the calibration tool 72 (morespecifically, to a reflection surface of the glass block of thecalibration tool 72 corresponding to the anterior surface of the cornea)match an optical path length from the Galvano scanner 62 to a reflectionsurface of the reference mirror 74 (more specifically, to a reflectionsurface of a glass block of the reference mirror 74 corresponding to theanterior surface of the cornea). Thus, so long as the optical pathlengths of the optical systems of the anterior part OCT 53 do notchange, a depthwise position of the reflection surface of thecalibration tool 72 matches a depthwise position of the reference mirror74. Similar to the first embodiment, a state in which the light from thelight source 82 is emitted to the subject eye (calibration tool 72) anda state in which the light from the light source 82 is emitted to thereference mirror 74 are switched by driving the Galvano scanner 62. Thelight emitted to the reference mirror 74 is reflected toward the Galvanoscanner 62, and is inputted to the coupler 88 through the beam splitter60, the lens 59, and the optical fiber 86 c.

The anterior part interference optical system comprises the coupler 88.The coupler 88 is configured to combine the light reflected from thecalibration tool 72 (or the subject eye 200) and the light reflectedfrom the reference mirror 92 and generate interference light, and tocombine the light reflected from the reference mirror 74 and the lightreflected from the reference mirror 92 and generate interference light.The interference light generated in the coupler 88 is inputted to theanterior part detector 84. The anterior part detector 84 is configuredto detect the interference light and outputs an interference signal to acontroller 100 (shown in FIG. 8 ).

The retina OCT 52 is an optical coherence tomographic device (SD-OCT)comprising a wide-band wavelength light source 54, and comprises aretina measurement optical system (58 a, 58 e, 55, 60, 62, 63, 66, 70,76, 78, 68), a first retina reference optical system (58 a, 58 c, 58 d,55, 61, 64), a second retina reference optical system (58 f, 61, 90, 96,92), a retina interference optical system 55, and a retina detector 56.

The retina measurement optical system comprises optical fibers 58 a, 58e, a coupler 55, the beam splitter 60, the Galvano scanner 62, mirrors63, 66, 70, the lenses 76, 78, and the mirror 68. Light outputted fromthe light source 54 travels through the optical fiber 58 a and is splitinto measurement light and third reference light in the coupler 55, andthe measurement light split in the coupler 55 is outputted from the endof the optical fiber 58 e toward the beam splitter 60. The lightoutputted from the optical fiber 58 e is reflected on the beam splitter60 and is outputted to the Galvano scanner 62. The light reflected onthe Galvano scanner 62 is reflected on the mirrors 63, 66, 70, reflectedon the mirror 68 through the lens 78, and is emitted onto the subjecteye 200 (calibration tool 72 in FIG. 5 ). The reflected light from thesubject eye 200 travels on the aforementioned path in an oppositedirection and is inputted to the coupler 55.

The first retina reference optical system comprises optical fibers 58 a,58 c, 58 d, a coupler 55, 61, and a reference mirror 64. The thirdreference light split in the coupler 55 travels through the opticalfiber 58 c and is inputted to the coupler 61. The coupler 61 splits thelight inputted from the optical fiber 58 c into third reference lightand fourth reference light (for example, third reference light: fourthreference light=99:1). The third reference light split in the coupler 61travels through the optical fiber 58 d and is outputted toward thereference mirror 64 from the end of the optical fiber 58 d. The lightoutputted to the reference mirror 64 and reflected thereon travels onthe aforementioned path in an opposite direction and is inputted to thecoupler 55.

The second retina reference optical system has an optical path branchingfrom the coupler 61 of the first retina reference optical system, andincludes the coupler 61, an optical fiber 58 f, a beam splitter 90, alens 96, and a reference mirror 92 (the reference mirror 92 in theanterior part OCT 53). That is, the reference mirror 92 of the secondretina reference optical system and the reference mirror 92 of the firstanterior part reference optical system are a shared component. Thefourth reference light split in the coupler 61 is emitted to thereference mirror 92 through the optical fiber 58 f, the beam splitter90, and the lens 96, and is reflected on the reference mirror 92. Thefourth reference light reflected on the reference mirror 92 is inputtedto the lens 96, the beam splitter 90, the optical fiber 58 f, and thecoupler 61. In the coupler 61, the third reference light reflected onthe reference mirror 64 and the fourth reference light reflected on thereference mirror 92 are combined.

The retina interference optical system comprises the coupler 55. Thecoupler 55 combines the light inputted from the optical fiber 58 c (thatis, the third reference light reflected on the reference mirror 64 andthe fourth reference light reflected on the reference mirror 92) and thelight inputted from the optical fiber 58 e (measurement light reflectedon the subject eye). Due to this, interference light generated from thethird reference light reflected on the reference mirror 64 and themeasurement light reflected on the subject eye 200, interference lightgenerated from the third reference light reflected on the referencemirror 64 and the fourth reference light reflected on the referencemirror 92, and interference light generated from the fourth referencelight reflected on the reference mirror 92 and the measurement lightreflected on the subject eye 200 are thereby generated. The generatedinterference light is inputted to the retina detector 56 through theoptical fiber 58 b. Here, an intensity of the fourth reference light isset to an intensity that is small enough that it can be ignored ascompared to an intensity of the third reference light. Due to this, theretina detector 56 detects the interference light generated from thethird reference light reflected on the reference mirror 64 and themeasurement light reflected on the subject eye and also the interferencelight generated from the third reference light reflected on thereference mirror 64 and the fourth reference light reflected on thereference mirror 92, and outputs interference signals of theinterference light as above to the controller 100 (shown in FIG. 8 ) tobe described later.

Next, the configuration of a control system of the ophthalmic device 50will be described. As shown in FIG. 8 , the ophthalmic device 50 iscontrolled by the controller 100. The controller 100 is configured of amicrocomputer (microprocessor) configured of, for example, a CPU, a ROM,and a RAM, and functions as a computing unit 102 and a storage unit 104similar to the first embodiment. The controller 100 includes the lightsources 54, 82, the detectors 56, 84, and the Galvano scanner 62connected thereto. The controller 100 is configured to control on/off ofthe light sources 54, 82 and also drive the Galvano scanner 62. Further,the controller 100 is configured to generate tomographic images of thesubject eye 200 based on the interference signals inputted from thedetectors 56, 84.

In the second embodiment, the controller 100 further includes ananterior part reference optical path length adjuster 106 and a retinareference optical path length adjuster 108 connected thereto. That is,in the second embodiment, a length from the end of the optical fiber 86d to the reference mirror 92 is adjustable, and a length from the end ofthe optical fiber 58 d to the reference mirror 64 is adjustable. Thecontroller 100 drives the anterior part reference optical path lengthadjuster 106 to move the lens 94, the beam splitter 90, the lens 96, andthe reference mirror 92 in an optical axis direction with respect to theend of the optical fiber 86 d. Further, the controller 100 drives theretina reference optical path length adjuster 108 to move the lensreference mirror 64 in the optical axis direction with respect to theend of the optical fiber 58 d.

Further, the storage unit 104 of the controller 100 stores various typesof information used for measuring the axial length of the subject eye200. That is, in the ophthalmic device 50 of the second embodiment, asshown in FIG. 5 , the calibration process is performed using thecalibration tool 72 at the time of shipping, and various types ofinformation obtained in this calibration process is stored in thestorage unit 104. Specifically, the calibration tool 72 is arranged atthe position of the subject eye 200, and positions of the front and rearsurfaces of the glass block arranged at the position of the frontsurface of the calibration tool 72 (corresponding to the cornealsurface) and the front and rear surfaces of the glass block arranged atthe rear surface of the calibration tool 72 (corresponding to theretinal surface) are measured. That is, the positions of the front andrear surfaces of the glass block of the front surface of the calibrationtool 72 (corresponding to the corneal surface) are measured using theanterior part OCT 53, and the positions of the front and rear surfacesof the glass block of the rear surface of the calibration tool 72(corresponding to the retinal surface) are measured using the retina OCT52. In doing so, the anterior part OCT 53 measures the position of thereflection surface of the reference mirror 74 in the second anteriorpart reference optical system. Further, the retina OCT 52 measures theposition of the reference mirror 92 of the second retina referenceoptical system (that is, the reference mirror 92 in the first anteriorpart reference optical system of the anterior part OCT 53).

Here, the length from the front surface to the rear surface of thecalibration tool 72 is known, thus similar to the first embodiment, thecomputing unit 102 of the controller 100 calculates conversion formulasand a positional relationship (length A) for calculating the axiallength of the subject eye 200 (actual length thereof) from the positionof the anterior surface of the cornea identified from the imagescaptured in the anterior part OCT 53 and the position of the retinalsurface identified from the images captured in the retina OCT 52. Then,the storage unit 104 of the controller 100 stores the calculatedconversion formulas and positional relationship (length A). Further, thestorage unit 104 of the controller 100 stores the measured position ofthe front surface of the calibration tool 72 (that is, the position ofthe reference mirror 74 in the second anterior part reference opticalsystem) and the measured position of the reference mirror 92 (that is,the position of the reference mirror 92 in the second retina referenceoptical system).

Next, operation of the ophthalmic device 50 at the time of measuring theaxial length of the subject eye 200 will be described. Firstly, afterthe optical systems of the anterior part OCT 53 and the retina OCT 52are positioned with respect to the subject eye 200, the controller 100turns on the light sources 54, 82 as shown in FIG. 9 (S20).

Then, the controller 100 measures the position of the reference mirror74 and the position of the reference mirror 92 (S22). Specifically, asshown in FIG. 6 , the light from the light source 54 is emitted to thereference mirror 92, and the light from the light source 82 is emittedto the reference mirror 74 by driving the Galvano scanner 62. By doingso, the retina detector 56 detects the interference light that isgenerated from the reflected light reflected on the reference mirror 92and the third reference light (third reference light in the first retinareference optical system), and the controller 100 calculates theposition of the reference mirror 92 (reference mirror 92 in the firstanterior part reference optical system) from the interference lightdetected by the retina detector 56. Further, the anterior part detector84 detects the interference light that is generated from the reflectedlight reflected on the reference mirror 74 and the first reference light(first reference light in the first anterior part reference opticalsystem), and the controller 100 calculates the position of the referencemirror 74 from the interference light detected by the anterior partdetector 84.

Next, the controller 100 adjusts the optical path length of the firstanterior part reference optical system and the optical path length ofthe first retina reference optical system based on the positions of thereference mirrors 74, 92 stored in the storage unit 104 and thepositions of the reference mirrors 74, 92 measured in S22 (S24). Asalready described, the position of the front surface of the calibrationtool 72 (that is, the position of the reference mirror 74) and theposition of the reference mirror 92 are already measured in thecalibration process at the time of shipment, and these are stored in thestorage unit 104. The optical path lengths of the optical systems of theophthalmic device 50 change from their values at the time of shipment(the time at which the calibration process is performed) due to thepost-shipment chronological change and the environment temperature ofthe ophthalmic device 50. Due to this, in S24, the anterior partreference optical path length adjuster 106 adjusts the position of thereference mirror 92 so that the position of the reference mirror 92measured in S22 matches the position of the reference mirror 92 storedin the storage unit 104. Next, the position of the reference mirror 64is adjusted by the retina reference optical path length adjuster 108 sothat the position of the reference mirror 74 measured in S22 matches theposition of the front surface of the calibration tool 72 stored in thestorage unit 104. At this occasion, since the position of the referencemirror 92 has already been adjusted, the position of the referencemirror 74 measured in S22 has changed according to this adjustment. Dueto this, the position of the reference mirror 64 is adjusted based onthe amount of the position adjustment of the reference mirror 92 and theposition of the reference mirror 74 measured in S22. Due to this, adepthwise positional relationship of an imaging range 202 a of theanterior part OCT 53 and an imaging range 204 a of the retina OCT 52matches the positional relationship at the time of the calibrationprocess.

Next, as shown in FIG. 7 , the controller 100 measures the position ofthe corneal surface of the subject eye 200 using the anterior part OCT53 and measures the position of the retinal surface using the retina OCT52 (S26). Then, the controller 100 uses the measurement results of S26(the position of the corneal surface and the position of the retinalsurface) and the conversion formulas and the positional relationship(length A) stored in the storage unit to calculate the axial length ofthe subject eye 200 (S28). Here, by S24, the depthwise positionalrelationship of the imaging range 202 a of the anterior part OCT 53 andthe imaging range 204 a of the retina OCT 52 become identical to thepositional relationship at the time of the calibration process. Due tothis, the axial length can be calculated using the conversion formulasand the positional relationship (length A) stored in the storage unitwithout correcting the position of the corneal surface and the positionof the retinal surface measured in S26.

In the ophthalmic device 50 of the second embodiment as above, the axiallength of the subject eye 200 can be measured in the same state as thestate at the time of the calibration by adjusting the optical pathlengths of the optical systems of the anterior part OCT 53 and theretina OCT 52. Due to this, the ophthalmic device 50 of the secondembodiment can also measure the axial length of the subject eye 200 withhigh accuracy.

Further, in the ophthalmic device 50 of the second embodiment as well,the measurement of the subject eye 200 is performed with the anteriorpart OCT 53 after the measurement of the reference mirror 74 has beencompleted. That is, since the measurement of the reference mirror 74 andthe measurement of the subject eye 200 are not performed simultaneously,the position of the reference mirror 74 can be set to a desiredposition.

In the ophthalmic device 50 of the second embodiment as above, thereference optical path length of the first anterior part referenceoptical system in the anterior part OCT 53 as well as the referenceoptical path length of the first retina reference optical system in theretina OCT 52 are adjusted such that the positional relationship of theanterior part OCT 53 and the retina OCT 52 matches the positionalrelationship in the calibration process, however, the art disclosedherein is not limited to such an example. For example, only thereference optical path length of the first anterior part referenceoptical system in the anterior part OCT 53 may be adjusted such that thepositional relationship of the anterior part OCT 53 and the retina OCT52 matches the positional relationship in the calibration process.Alternatively, the positional relationship of the anterior part OCT 53and the retina OCT 52 may be set to match the positional relationship inthe calibration process by adjusting only the reference optical pathlength of the first retina reference optical system in the retina OCT52.

Further, in the ophthalmic device 50 of the second embodiment, the thirdreference light in the retina OCT 52 is split to generate fourthreference light, and the generated fourth reference light is emitted tothe reference mirror 92, however, the art disclosed herein is notlimited to such an example. Contrary to the aforementioned example, thefirst reference light in the anterior part OCT may be split to generatethe second reference light, and this generated second reference lightmay be emitted to the reference mirror 64.

Further, the ophthalmic devices in the first and second embodiments asabove each comprise both the retina OCT and the anterior part OCT,however, the art disclosed herein may be applied to ophthalmic devicesthat comprise only the retina OCT or the anterior part OCT. In such acase, for example, a state in which light from a light source is emittedto a reference mirror and a state in which the light from the lightsource is emitted to the subject eye can be switched using a Galvanoscanner, by which the reference mirror can be set to a desired position.

Specific examples of the disclosure herein have been described indetail, however, these are mere exemplary indications and thus do notlimit the scope of the claims. The art described in the claims includesmodifications and variations of the specific examples presented above.Technical features described in the description and the drawings maytechnically be useful alone or in various combinations, and are notlimited to the combinations as originally claimed. Further, the purposeof the examples illustrated by the present description or drawings is tosatisfy multiple objectives simultaneously, and satisfying any one ofthose objectives gives technical utility to the present disclosure.

What is claimed is:
 1. An ophthalmic device comprising: a light source;a measurement optical system configured to generate measurement light byirradiating a subject eye with light from the light source; a firstreference optical system configured to generate first reference light byusing the light from the light source; a second reference optical systemconfigured to generate second reference light by using the light fromthe light source, the second reference light being used for calculatinga reference position; an interference optical system configured togenerate measurement interference light by combining the measurementlight and the first reference light and to generate referenceinterference light by combining the second reference light and the firstreference light; a detector configured to detect the measurementinterference light and output a measurement interference signal and todetect the reference interference light and output a referenceinterference signal; and a controller configured to calculate depthwiseposition information of the subject eye based on the measurementinterference signal and to calculate the reference position based on thereference interference signal, wherein the second reference opticalsystem includes an optical path branching from the measurement opticalsystem, the measurement optical system comprises a switching unitconfigured to switch between a first state and a second state, the firststate being a state in which the subject eye is irradiated with thelight from the light source and the second state being a state in whichthe light from the light source is guided to the second referenceoptical system, and when the subject eye is measured, the controller isconfigured to control the switching unit to detect the measurementinterference light with the detector in the first state, and to detectthe reference interference light with the detector in the second state.2. The ophthalmic device according to claim 1, wherein the controller isconfigured to control the switching unit to detect the referenceinterference signal with the detector in the second state before orafter detecting the measurement interference light with the detector inthe first state.
 3. The ophthalmic device according to claim 1, furthercomprising a storage unit configured to store a specific-time referenceposition indicating the reference position adjusted at a specific time,the specific-time reference position being a position calculated fromthe reference interference light generated by combining the secondreference light generated in the second reference optical system and thefirst reference light generated in the first reference optical system atthe specific time, wherein the controller is configured to correct thedepthwise position information of the subject eye calculated based onthe measurement interference signal outputted from the detector when thesubject eye is measured, the depthwise position information beingcorrected based on a difference between a measurement-time referenceposition and the specific-time reference position stored in the storageunit, the measurement-time reference position being the referenceposition calculated based on the reference interference signal outputtedfrom the detector when the subject eye is measured.
 4. The ophthalmicdevice according to claim 3, wherein the storage unit is configured tofurther store a conversion formula for converting the depthwise positioninformation of the subject eye calculated based on the measurementinterference signal to an actual measurement of the subject eye, thecontroller is configured to further calculate the actual measurement ofthe subject eye by converting the depthwise position information of thesubject eye calculated based on the measurement interference signal withthe conversion formula, and the conversion formula is obtained by using(A) depthwise position information of at least two reflection surfacesof a calibration tool having a known optical path length difference and(B) the optical path length difference between the at least tworeflection surfaces, the depthwise position information of the at leasttwo reflection surfaces being obtained from calibration interferencelight generated by combining calibration measurement light and the firstreference light generated in the first reference optical system, thecalibration measurement light being generated by irradiating thecalibration tool from the measurement optical system with the light fromthe light source.
 5. The ophthalmic device according to claim 4, whereinthe specific time and a time at which the calibration interference lightis measured by using the calibration tool to obtain the conversionformula are substantially simultaneous.
 6. The ophthalmic deviceaccording to claim 1, further comprising a storage unit configured tostore a specific-time reference position indicating the referenceposition adjusted at a specific time, the specific-time referenceposition being a position calculated from the reference interferencelight generated by combining the second reference light generated in thesecond reference optical system and the first reference light generatedin the first reference optical system at the specific time, wherein thefirst reference optical system comprises an adjuster configured toadjust an optical path length of the first reference light, and thecontroller is configured to calculate a measurement-time referenceposition that is the reference position calculated based on thereference interference signal outputted from the detector when thesubject eye is measured and to control the adjuster so that themeasurement-time reference position calculated when the subject eye ismeasured matches the specific-time reference position stored in thestorage unit.
 7. The ophthalmic device according to claim 6, wherein thestorage unit is configured to further store a conversion formula forconverting the depthwise position information of the subject eyecalculated based on the measurement interference signal to an actualmeasurement of the subject eye, the controller is configured to furthercalculate the actual measurement of the subject eye by converting thedepthwise position information of the subject eye calculated based onthe measurement interference signal with the conversion formula, and theconversion formula is obtained by using (A) depthwise positioninformation of at least two reflection surfaces of a calibration toolhaving a known optical path length difference and (B) the optical pathlength difference between the at least two reflection surfaces, thedepthwise position information of the at least two reflection surfacesbeing obtained from calibration interference light generated bycombining calibration measurement light and the first reference lightgenerated in the first reference optical system, the calibrationmeasurement light being generated by irradiating the calibration toolfrom the measurement optical system with the light from the lightsource.
 8. The ophthalmic device according to claim 7, wherein thespecific time and a time at which the calibration interference light ismeasured by using the calibration tool to obtain the conversion formulaare substantially simultaneous.
 9. The ophthalmic device according toclaim 6, wherein the controller is configured to: detect the referenceinterference light with the detector while the switching unit is in thesecond state; control the adjuster so that the measurement-timereference position calculated based on the reference interference signaloutputted from the detector matches the specific-time reference positionstored in the storage unit; and detect the measurement interferencelight while the switching unit is in the first state after the opticalpath length of the first reference light is adjusted by the adjuster.10. An ophthalmic device comprising: a first OCT configured to measure afirst depthwise position of a first part of a subject eye; a second OCTconfigured to measure a second depthwise position of a second part ofthe subject eye, the second part being different from the first part;and a controller configured to calculate a depthwise length from thefirst part to the second part based on the first depthwise positionmeasured by the first OCT and the second depthwise position measured bythe second OCT, wherein the first OCT comprises: a first light source; afirst measurement optical system configured to generate firstmeasurement light by irradiating the first part of the subject eye withlight from the first light source; a first reference optical systemconfigured to generate first reference light by using the light from thefirst light source; a second reference optical system configured togenerate second reference light by using the light from the first lightsource, the second reference light being used for calculating a firstreference position; a first interference optical system configured togenerate first measurement interference light by combining the firstmeasurement light and the first reference light and to generate firstreference interference light by combining the second reference light andthe first reference light; and a first detector configured to detect thefirst measurement interference light and output a first measurementinterference signal and to detect the first reference interference lightand output a first reference interference signal, wherein the secondreference optical system includes an optical path branching from thefirst measurement optical system, the first measurement optical systemcomprises a first switching unit configured to switch between a firststate and a second state, the first state being a state in which thesubject eye is irradiated with the light from the first light source andthe second state being a state in which the light from the first lightsource is guided to the second reference optical system, and when thesubject eye is measured, the first detector is configured to detect thefirst measurement interference light while the first switching unit isin the first state, and to detect the first reference interference lightwhile the first switching unit is in the second state.
 11. Theophthalmic device according to claim 10, wherein the second OCTcomprises: a second light source; a second measurement optical systemconfigured to generate second measurement light by irradiating thesecond part of the subject eye with light from the second light source;a third reference optical system configured to generate third referencelight by using the light from the second light source; a fourthreference optical system configured to generate fourth reference lightby using the light from the second light source, the fourth referencelight being used for calculating a second reference position; a secondinterference optical system configured to generate second measurementinterference light by combining the second measurement light and thethird reference light and to generate second reference interferencelight by combining the fourth reference light and the third referencelight; and a second detector configured to detect the second measurementinterference light and output a second measurement interference signaland to detect the second reference interference light and output asecond reference interference signal, wherein the fourth referenceoptical system includes an optical path branching from the secondmeasurement optical system, the second measurement optical systemcomprises a second switching unit configured to switch between a thirdstate and a fourth state, the third state being a state in which thesubject eye is irradiated with the light from the second light sourceand the fourth state being a state in which the light from the secondlight source is guided to the fourth reference optical system, and whenthe subject eye is measured, the second detector is configured to detectthe second measurement interference light while the second switchingunit is in the third state, and to detect the second referenceinterference light while the second switching unit is in the fourthstate.
 12. The ophthalmic device according to claim 11, wherein when thefirst switching unit is switched to the first state, the secondswitching unit is switched to the third state, when the first switchingunit is switched to the second state, the second switching unit isswitched to the fourth state, and the first switching unit and thesecond switching unit are a single switching unit shared by the firstmeasurement optical system and the second measurement optical system.13. The ophthalmic device according to claim 11, further comprising astorage unit configured to store a depthwise distance between ameasurement area of the first OCT and a measurement area of the secondOCT adjusted at a specific time, a first specific-time referenceposition indicating the first reference position adjusted at thespecific time, and a second specific-time reference position indicatingthe second reference position adjusted at the specific time, wherein thecontroller is configured to calculate the depthwise length from thefirst part to the second part based on: (1) a difference between a firstmeasurement-time reference position and the first specific-timereference position stored in the storage unit, the firstmeasurement-time reference position being calculated based on the firstreference interference signal outputted from the first detector when thesubject eye is measured; (2) the first position of the subject eyecalculated based on the first measurement interference signal outputtedfrom the first detector when the subject eye is measured; (3) adifference between a second measurement-time reference position and thesecond specific-time reference position stored in the storage unit, thesecond measurement-time reference position being calculated based on thesecond reference interference signal outputted from the second detectorwhen the subject eye is measured; (4) the second position of the subjecteye calculated based on the second measurement interference signaloutputted from the second detector when the subject eye is measured; and(5) the depthwise distance between the measurement area of the first OCTand the measurement area of the second OCT stored in the storage unit.14. The ophthalmic device according to claim 13, wherein the storageunit is configured to further store: a first conversion formula forconverting depthwise position information of the subject eye calculatedbased on the first measurement interference signal to an actualmeasurement of the subject eye in the measurement area of the first OCT;and a second conversion formula for converting depthwise positioninformation of the subject eye calculated based on the secondmeasurement interference signal to an actual measurement of the subjecteye in the measurement area of the second OCT, wherein the controller isconfigured to further calculate the actual measurement of the subjecteye in the measurement area of the first OCT by converting the depthwiseposition information of the subject eye calculated based on the firstmeasurement interference signal with the first conversion formula, andto further calculate the actual measurement of the subject eye in themeasurement area of the second OCT by converting the depthwise positioninformation of the subject eye calculated based on the secondmeasurement interference signal with the second conversion formula, thefirst conversion formula is obtained by using (A1) depthwise positioninformation of at least two reflected surfaces of a first calibrationtool having a known an optical path length difference and (B1) theoptical path length difference between the at least two reflectedsurfaces, the depthwise position information of the at least tworeflected surfaces of the first calibration tool is obtained from firstcalibration interference light generated by combining first calibrationmeasurement light and first reference light generated in the firstreference optical system, the first calibration measurement light beinggenerated by irradiating the first calibration tool from the firstmeasurement optical system with the light from the first light source,and the second conversion formula is obtained by using (A2) depthwiseposition information of at least two reflected surfaces of a secondcalibration tool having a known optical path length difference and (B2)the optical path length difference between the at least two reflectedsurfaces, the depthwise position information of the at least tworeflected surfaces of the second calibration tool is obtained fromsecond calibration interference light generated by combining secondcalibration measurement light and third reference light generated in thethird reference optical system, the second calibration measurement lightis generated by irradiating the second calibration tool from the secondmeasurement optical system with the light from the second light source.15. The ophthalmic device according to claim 14, wherein the firstspecific-time reference position is a position calculated from the firstreference interference light generated by combining the second referencelight generated in the second reference optical system and the firstreference light generated in the first reference optical system at thespecific time, the second specific-time reference position is a positioncalculated from the second reference interference light generated bycombining the fourth reference light generated in the fourth referenceoptical system and the third reference light generated in the thirdreference optical system at the specific time, and the specific time, atime at which the first calibration tool is irradiated with the firstmeasurement light to obtain the first conversion formula and a time atwhich the second calibration tool is irradiated to the secondmeasurement light to obtain the second conversion formula aresubstantially simultaneous.
 16. The ophthalmic device according to claim11, further comprising an adjuster disposed on at least one of the firstreference optical system and the third reference optical system andconfigured to adjust an optical path length of the at least one of thefirst reference optical system and the third reference optical system,wherein the controller is configured to control the adjuster so that adistance between a first measurement-time reference position calculatedfrom the first reference interference signal when the subject eye ismeasured and a second measurement-time reference position calculatedfrom the second reference interference signal when the subject eye ismeasured matches a predetermined distance.
 17. The ophthalmic deviceaccording to claim 16, wherein the predetermined distance is a distancebetween a first specific-time reference position calculated from thefirst reference interference signal at a specific time and a secondspecific-time reference position calculated from the second referenceinterference signal at the specific time.
 18. The ophthalmic deviceaccording to claim 16, wherein the controller is configured to: detectthe first reference interference light with the first detector while thefirst switching unit is in the second state; detect the second referenceinterference light with the second detector while the second switchingunit is the fourth state; control the adjuster so that a differencebetween the first measurement-time reference position calculated basedon the first reference interference signal outputted from the firstdetector and the second measurement-time reference position calculatedbased on the second reference interference signal outputted from thesecond detector matches the predetermined distance, and after theoptical path length is adjusted by the adjuster, detect the firstmeasurement interference signal while the first switching unit is in thefirst state, and detect the second measurement interference signal whilethe second switching unit is in the third state.